Brain Advance Access published online on October 7, 2008
Brain, doi:10.1093/brain/awn242
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Striatal degeneration impairs language learning: evidence from Huntington's disease
1INSERM U841, Team 1: Interventional Neuropsychology, IM3-Paris 12, Créteil, France, 2ICREA and Department Basic Psychology, University of Barcelona, Barcelona, Spain, 3Département d’Études Cognitives, École Normale Supérieure, Paris and 4AP-HP, Centre de référence maladie de Huntington, Henri Mondor Hospital and Pitié Salpétrière Hospital, Créteil and Paris, France
Correspondence to:
Ruth de Diego-Balaguer, PhD, Departament de Psicologia Bàsica, Universitat de Barcelona, Pg. Vall d’Hebron, 171, 08035 Barcelona, Spain E-mail: ruth.dediego{at}icrea.cat
Although the role of the striatum in language processing is still largely unclear, a number of recent proposals have outlined its specific contribution. Different studies report evidence converging to a picture where the striatum may be involved in those aspects of rule-application requiring non-automatized behaviour. This is the main characteristic of the earliest phases of language acquisition that require the online detection of distant dependencies and the creation of syntactic categories by means of rule learning. Learning of sequences and categorization processes in non-language domains has been known to require striatal recruitment. Thus, we hypothesized that the striatum should play a prominent role in the extraction of rules in learning a language. We studied 13 pre-symptomatic gene-carriers and 22 early stage patients of Huntington's disease (pre-HD), both characterized by a progressive degeneration of the striatum and 21 late stage patients Huntington's disease (18 stage II, two stage III and one stage IV) where cortical degeneration accompanies striatal degeneration. When presented with a simplified artificial language where words and rules could be extracted, early stage Huntington's disease patients (stage I) were impaired in the learning test, demonstrating a greater impairment in rule than word learning compared to the 20 age- and education-matched controls. Huntington's disease patients at later stages were impaired both on word and rule learning. While spared in their overall performance, gene-carriers having learned a set of abstract artificial language rules were then impaired in the transfer of those rules to similar artificial language structures. The correlation analyses among several neuropsychological tests assessing executive function showed that rule learning correlated with tests requiring working memory and attentional control, while word learning correlated with a test involving episodic memory. These learning impairments significantly correlated with the bicaudate ratio. The overall results support striatal involvement in rule extraction from speech and suggest that language acquisition requires several aspects of memory and executive functions for word and rule learning.
Key Words: Huntington's disease; striatum; language; rule learning; executive control
Abbreviations: HD1, Huntington's disease patients at stage I; HD2, Huntington's disease patients at stages II, III and IV; MDRS, Mattis Dementia Rating Scale; pre-HD, pre-symptomatic Huntington's disease gene-carriers; TMT, Trail Making Test; UHDRS, Unified Huntington's Disease Rating Scale
Received January 31, 2008. Revised August 29, 2008. Accepted September 7, 2008.
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